Age is an interesting thing to look at especially in investing. I think that with practice you can accumulate knowledge from the past that is applicable to investments today. They often say that Buffett is a learning machine. He finds information that is worthwhile and files it away, only to use it later. This is probably most helpful when you start approaching investments that have more 'art' than science, think of all the crazy deals he has made. For younger investors, I would guess that things are much more process driven which is not necessarily bad. A disciplined young investor seeking out Graham-style investments will probably do well until they grow their assets in a way that makes those investments no longer viable. Then it becomes a matter of using your knowledge and more of the 'art'

Always wondered how I got stuck in the transition between being a chess expert and a chess master even though the hours of study and playing accumulated. An important part was loosing my mentor so most of the studying and practice was not focused where it was needed. And it is difficult to know what you do not know when you reach that level. The low hanging fruit has been taken.

I also wondered how age affects this process. In chess it used to be that you reach your top performance at your 40s. You have perfected your openings and reached positional understanding. However you are now seeing generation after generation of “prodigies” using computers to obliterate those advantages. Today's game is much more about tactics, solving mathematical puzzles where you reach your zenith in your 20s

Regarding the issue of process vs results, just look at poker where luck is even more important and you see the same guys time and again in the final tables. In chess I have beaten NMs and IMs, but the hit ratio is not that high. The same with investing.

I still think that I could have beaten Henry Singleton though.

Becoming a good investor requires time and effort. It is not easy, but just learning to avoid simple errors can improve investment results dramatically — there are enough promising situations — if an investment seems too complex, move on. Don't anything that you can't understand. When you do investments that you do not understand, you will not know when to buy and sell.

However, there are certain activities in which practise is of little value, and investing is probably one of them. If you buy a stock based on your analysis and the stock goes up, you can conclude that this is because your thinking was sound. And the fact that the stock went up may have nothing to do with your analysis. This is why the feedback your get from investing is so different than the feedback your get from chess.

To be succesful at investing, we need to learn to think about processes instead of stocks. This is why we should as investors think about creating a set of empirically based rules for the purpose of selecting stocks, instead of thinking about stocks themselves. We can back test these rules on different sets of data. This way we will avoid emotional investing and the overconfidence that has led to many top advisors to have too much faith in their own abilities.